The prevalence of the MAOA µVNTR alleles and their relationship to childhood behaviour and personality within a South African cohort

Abstract

Historically, the X-linked monoamine oxidase A promoter variable number tandem repeat (MAOA µVNTR) low-activity (versus high-activity) alleles were thought to be associated with an increase in internalising and externalising behaviour problems in males. However, recent research has highlighted the importance of gene-environment (GxE) interactions as a modifier of this effect. Individuals with a low-activity allele, who were raised in a poor environment, show higher levels of behavioural problems, however, when these same individuals are in a supportive environment, they experience the lowest levels of behavioural problems compared to high-activity allele individuals. These crossover effects have been recently incorporated into a theory known as Environmental Sensitivity. This study aimed to genotype the MAOA µVNTR by PCR and gel electrophoresis within South African males (n = 543) and females (n = 593) of the Birth to Twenty Plus cohort. Genotypes were then correlated to historical cohort data on caregiver-rated childhood behaviour from the South African Child Assessment Schedule. When accounting for covariates (5-HTTLPR, gestational age, birth weight, maternal education, and household socio-economic status), linear regression analysis revealed that possessing a low-activity MAOA µVNTR allele was a predictor of internalising behaviour in males (p < 0.05) and females (p < 0.05) and externalising behaviour (p < 0.05) in males, but not sensory processing sensitivity (a psychological marker of environmental sensitivity) in either males (p > 0.1) or females (p > 0.1). Additionally, when maternal education was applied as an environmental modifier, a significant interaction (p < 0.01) revealed that males with a low-activity MAOA allele have externalising behavioural scores in direct proportion to maternal education levels. Moreover, males without a high-activity allele showed no change in externalising behaviour as a function of maternal education. When household socio-economic status was used as the environmental modifier in females, a significant interaction (p < 0.01) revealed a contrasting effect where low-activity allele carriers experienced an increase in internalising behaviour problems with an improved environment. However, high-activity allele carriers experience the opposite. These findings support the role of Environmental Sensitivity

theory through GxE interaction models in predicting behavioural development.